a) Field of the Invention
The present invention relates to a vacuum cleaner with a cyclonic dust collection device, particularly to a structure of such dust collection device.
b) Prior Art
Conventional cyclonic cleaners of this type are disclosed for example in Japanese Un-Examined Patent Publication No. 2000-135183. The disclosed vacuum cleaner comprises: a cleaner body with an electric fan unit (a fan unit); a front end pipe (a vacuum pipe) including a floor suction nozzle (suction hole) at its tip end; a first air path defined by the floor suction nozzle and the front end pipe; a second air path defined by a joint pipe and a hose; and a cyclonic separation type dust collection device attached to between the first and the second air paths. Thus, an airflow is generated by actuating the electric fan unit so that dusts are sucked from the floor suction nozzle together with the airflow, thus generating a vortex flow along an inside surface of a cylindrical dust collecting portion (or dust collection container) that constructs the aforesaid cyclonic dust collection device. This vortex flow falls down toward a bottom plate of the cylindrical dust-collecting portion, while the dusts included in the vortex flow are allowed to whirl round along the inside surface thereof due to a centrifugal force, whereby the dusts are collected in a bottom portion by such centrifugal force and downwardly-directing force developed by the descending vortex flow. The vortex flow from which the dusts were removed thus way is then allowed to rise up from near the center of the bottom plate of the said cylindrical dust collection portion to thereby be discharged to the outside of the cyclonic separation type dust collection device from a vent hole formed at an end of a rear end pipe.
According to the conventional cyclonic vacuum cleaner, however, fine or comparatively light dusts also are allowed to ascend together with the vortex flow, which, in association with the fact that the vent hole of the rear end pipe is opposite to the bottom plate of the cylindrical dust collecting portion, are likely to be discharged from the vent hole to the outside of the cyclonic separation dust collection device. A known solution for such problem is to cover the vent hole with a meshed member such as a filter. In that case, however, such filter is liable to be clogged with loose dust and the like, thus lowering the vacuum efficiency of an electric fan unit.